PSR-12: Extended Coding Style

Extended Coding Style Guide Meta Document

1. Summary

This document describes the process and discussions that led to the Extended Coding Style PSR. Its goal is to explain the reasons behind each decision.

2. Why Bother?

PSR-2 was accepted in 2012 and since then a number of changes have been made to PHP, most notably recent changes for PHP 7, which have implications for coding style guidelines. Whilst PSR-2 is very comprehensive of PHP functionality that existed at the time of writing, new functionality is very open to interpretation. PSR-12 seeks to provide a set way that both coding style tools can implement, projects can declare adherence to and developers can easily relate on between different projects for these coding style reducing cognitive friction.

PSR-2 was created based upon the common practices of the PHP-FIG projects at the time but ultimately this meant it was a compromise of many of the different projects' guidelines. The repercussions of projects changing their coding guidelines to align with PSR-2 (Almost all projects do align with PSR-1, even if it is not explicitly stated) were seen to be too great (losing git history, huge changesets and breaking existing patches/pull requests).

PSR-2 required adopters to reformat large amounts of existing code which stifled adoption. To help alleviate this issue with PSR-12, we have taken a more prescriptive approach and defined the standards for new language features as they are released.

However it is for a lack of wanting to be dictatorial that we will aim to apply PSR-2 styling, rationale and stances (Described in Section 4, Approaches) in PSR-12 instead of establishing new conventions.

3. Scope

3.1. Goals

This PSR shares the same goals as PSR-2.

The intent of this guide is to reduce cognitive friction when scanning code from different authors. It does so by enumerating a shared set of rules and expectations about how to format PHP code. When various authors collaborate across multiple projects, it helps to have one set of guidelines to be used among all those projects. Thus, the benefit of this guide is not in the rules themselves, but in the sharing of those rules.

This PSR is an extension of PSR-2, and therefore also an extension of PSR-1. The basis of PSR-12 is PSR-2 and therefore a list of differences is provided below to assist with migration but it should be considered as an independent specification.

This PSR will include coding style guidelines related to new functionality added to PHP after the publication of PSR-2; this includes PHP 5.5, PHP 5.6 and PHP 7.0. This PSR will also include clarifications on the text of PSR-2, as described in the PSR-2 Errata.

3.2. Non-Goals

It is not the intention of this PSR to add entirely new coding style guidelines. PSR-12 will also not change anything stipulated in PSR-1 and PSR-2.

4. Approaches

The overarching approach is to attempt to apply existing PSR-2 styling and rationale to new functionality as opposed to establishing new conventions.

4.1. Strict Types Declarations

There was a discussion about whether or not strict types should be enforced in the standard All were in agreement we should only use a MUST or MUST NOT statement and avoid the use of a SHOULD statement and nobody wanted to say that strict types could not be declared. The discussion was whether it should be considered a coding style item which should be covered or whether it was out of scope and it was decided to be out of scope of a coding style guide.

4.2. Finally and Return Types Declaration Spacing

Numerous different options were suggested and they can be seen here for return type declarations or here for finally blocks and the current implementation was chosen due to consistency with other parts of the PSR-12 specification that came from PSR-2.

4.3. Enforcing short form for all type keywords

PHP 7.0 introduced scalar types declaration which does not support long type aliases. Therefore it makes sense to enforce primary short type forms to be used to have uniform syntax and prevent possible confusion.

4.4. Public Survey

In order to settle things using data, survey was conducted and responses from 142 people including 17 project representatives were gathered:

4.4.1. PHP-FIG Representative Results

Representative Project Compound namespaces with a depth of two or more MUST not be used Header statement grouping and ordering Declare statements must each be on their own line Declare statements in PHP files containing markup Declare statements have no spaces: declare(strict_types=1); Block declare statement formatting new keyword usage, parenthesis required Return type declaration formatting Use statement leading slashes disallowed Block namespace declaration formatting General operator spacing Try, Catch, Finally formatting Anonymous class declaration formatting Keyword casing, only lower case Type keywords, short form only
Alexander Makarov Yii framework
Korvin Szanto concrete5
Leo Feyer Contao
Larry Garfield Drupal
André R. eZ
Jan Schneider Horde
Karsten Dambekalns Neos and Flow
Andres Gutierrez Phalcon
Ryan Thompson PyroCMS
Matteo Beccati Revive Adserver
Damian Mooyman SilverStripe
Brian Retterer Stormpath PHP SDK
Matthew Weier O'Phinney Zend Framework
Jordi Boggiano Composer
Ben Marks Magento
Chuck Burgess PEAR
Totals: 13/3 15/1 15/1 13/3 14/2 15/1 14/2 15/1 14/2 14/2 15/1 16/0 15/1 15/1 15/1

4.4.2. General non-representative voters

Question For Against Percentage For
Compound namespaces required depth 114 12 89.47%
Header statement grouping and ordering 113 13 88.5%
Declare statements must each be on their own line 120 6 95%
Declare statements in PHP files containing markup 119 7 94.12%
Declare statements have no spaces 116 10 91.38%
Block declare statement formatting 118 8 93.22%
new keyword usage, parenthesis required 116 10 91.38%
Return type declaration formatting 115 11 90.43%
Use statement leading slashes disallowed 118 8 93.22%
Block namespace declaration formatting 120 6 95%
General operator spacing 123 3 97.56%
Try, Catch, Finally formatting 124 2 98.39%
Anonymous class declaration formatting 117 9 92.31%
Keyword casing, only lower case 124 2 98.39%
Type keywords, short form only 121 5 95.87%

4.5. Multiline Function Arguments Mixed With Multiline Return

A potential readability issue was raised on the mailing list. We reviewed options for changes to the specification that could provide better readability and the floated option was to require a blank line after the opening bracket of a function if the arguments and the return are both multiline. Instead it was pointed out that this specification already allows you to decide where you'd like to add blank lines and so we will leave it to the implementors to decide.

5. Changelog from PSR-2

Please note this changelog is not a verbose list of changes from PSR-2 but highlights the most notable changes. It should be considered a new specification and therefore you should read the specification for a full understanding of its contents.

5.1. New Statements

  • Lowercase for all keywords - Section 2.5
  • Short form for all type keywords - Section 2.5
  • Use statement grouping - Section 3
  • Use statement blocks - Section 3
  • Declare statement/Strict types declaration usage - Section 3
  • Parentheses are always required for class instantiation - Section 4
  • Typed properties - Section 4.3
  • Return type declarations - Section 4.5
  • Variadic and reference argument operators - Section 4.5
  • Type hints - Section 4.5
  • Add finally block - Section 5.6
  • Operators - Section 6
  • Unary operators - Section 6.1
  • Binary operators - Section 6.2
  • Ternary operators - Section 6.3
  • Anonymous classes - Section 8

5.2. Clarifications and Errata

  • Adjust 'methods' to 'methods and functions' in a number of instances - Throughout
  • Adjust references to classes and interfaces to also include traits - Throughout
  • StudlyCaps meaning clarified as PascalCase - Section 2.1
  • The last line should not be blank but contain an EOL character - Section 2.2
  • Blank lines may be added for readability except where explicitly forbidden within the PSR - Section 2.3
  • PSR-2 errata statement about multi-line arguments - Section 4
  • PSR-2 errata statement about extending multiple interfaces - Section 4
  • Forbid blank lines before/after closing/opening braces for classes - Section 4

6. People

6.1. Editor:

  • Korvin Szanto

6.2. Sponsor:

  • Chris Tankersley

6.3. Working Group Members:

  • Alessandro Lai
  • Alexander Makarov
  • Michael Cullum
  • Robert Deutz

6.4. Special Thanks

  • Michael Cullum for drafting the original specification
  • Alexandar Makarov for coordinating the draft during PHP-FIG 2.0
  • Cees-Jan Kiewiet for moral support

7. Votes

  • Entrance Vote:!msg/php-fig/P9atZLOcUBM/_jwkvlYKEAAJ
  • Approval Vote:!topic/php-fig/1uaeSMaDGbk

8. Relevant Links

Note: Order descending chronologically.